piyo_piyo_(phrase)
An onomatopoetic Japanese phrase piyo piyo suru {ピヨピヨする} which means to make a chirping or cheeping sound. A sound you would normally expect from a chickidee. It is roughly translatable to the "spring of adolescence", where people are carefree and happy-go-lucky. The most familiar use of this phrase is the piyo piyo apron worn by Otonashi Kyouko, one of the main characters from Maison Ikkoku. It is believed by fans of the series to symbolize some kind of immaturity or refusal to move on in life.